In an LTE-A system, user equipment (UE, which may also be referred to as a terminal) communicates with a base station mainly via an air interface. An air interface protocol includes a control plane and a data plane (or may be named as a user plane); wherein, the control plane is mainly used to generate and transmit control information of the air interface, and the user plane is mainly used to transmit user data.
FIG. 1 is a schematic diagram of a structure of the control plane protocol between the UE and the base station, and FIG. 2 is a schematic diagram of a structure of the user plane protocol between the UE and the base station. As shown in FIGS. 1 and 2, the UE side has a corresponding MAC layer, no matter it is a user plane or a control plane. Actually, in a particular implementation of equipment, the MAC layer is shared by the user plane and the control plane.
FIG. 3 is a schematic diagram of a structure of the MAC layer at the UE side. As shown in FIG. 3, a rightmost control module controls all other entities in the MAC layer. A random access control module at the lower right side controls a random access procedure. A hybrid automatic repeat request (HARQ) module at the lower left side performs uplink and downlink HARQ operations. A (de)multiplexing module at the middle is dual connectivity, in a downlink, performs de-multiplexing on an MAC protocol data unit (PDU), after completion of the de-multiplexing, transmits related data to a corresponding downlink CCCH, a downlink DCCH and a downlink DTCH, and in an uplink, performs multiplexing on data from an uplink CCCH, an uplink DCCH and an uplink DTCH and MAC layer control information elements, so as to generate the MAC PDU. A leftmost de-multiplexing module is only for a downlink, performs de-multiplexing on data transmitted by an MCH, and transmits respectively to an MCCH and an MTCH. And an upmost logical channel prioritization module is only for an uplink, and processes data and MAC layer control information elements from different logical channels by using different priorities according to a prioritization rule.
In an existing LTE-A CA system, there are mainly two operations on an MAC layer: reconfiguration and resetting. During reconfiguration, related configurations of the MAC layer are increased, modified or deleted; for example, during the reconfiguration, if a secondary cell is increased, the MAC layer needs to initialize a corresponding HARQ entity, because each secondary cell needs different HARQ entities. When a secondary cell is removed, a corresponding HARQ entity should also be removed, as if this HARQ entity is not removed, a resource of the UE will be occupied. During resetting of the MAC layer, a timer of the MAC layer is stopped, and all related procedures are performed such operations as cancellation, etc, with a main object being to make settings of the MAC layer be in an initial known state. However, during the resetting, such operations as initialization or removal, etc., like those performed on an HARQ entity, are not performed on other entities in the MAC layer; that is, the entities other than the HARQ entities in the MAC layer still exist after resetting of the MAC layer. Viewing the MAC layer as a whole, after resetting of the MAC layer, the MAC entity still exists.
In an LTE-A system, the UE has two states: a connected state and an idle state. In the connected state, the UE may exchange specific data with the network side; and in the idle state, the UE may only receive broadcast or multicast data from the network side. When the UE is transferred from the idle state to the connected state, the network side needs to configure the UE with multiple specific radio resources, and the UE itself also needs to configure the connected state with specific resources, such as establishing related entities and starting a related timer; on the contrary, when the UE is transferred from the connected state to the idle state, all the specific radio resources and the specific resources at the UE need to be released.
In non-patent document 1, actions of the UE in leaving the connected state are provided, including: resetting an MAC entity; stopping all other timers in operation other than T320, T325 and T330; and releasing all radio resources, including releasing all radio link control (RLC) entities where radio bearer has been established, MAC configuration, and associated packet data converge protocol (PDCP) entities, etc. It can be seen that when the UE leaves the connected state, all the other entities in the MAC layer other than the HARQ entity are not released or removed.
On the other hand, in a current LTE-A system, a macro cell is mainly deployed. As the increase of traffics in the future, in order to perform system payload bridging or expansion coverage, it is possible that small cells (such as micro cells or pico cells, femto cells, and remote radio heads (RRHs), etc.) are deployed. Covered areas of small cells are relatively small, but the number of them is relatively large.
However, it was found by the inventors that if deployment of a small cell is only performed simply, with no optimization of control, many problems shall be produced, such as multiple times of handover, increase of rate of drops, and increase of load of control signaling, etc. And if an existing protocol is followed, no an MAC entity shall be deleted or removed. How to establish or delete more than one piece of connectivity has not been studied in the prior art. Therefore, reduction of waste of UE resources on the basis of control optimization cannot be ensured, nor a processing ability of the UE can further be efficiently increased.
It should be noted that the above description of the background is merely provided for clear and complete explanation of the present disclosure and for easy understanding by those skilled in the art. And it should not be understood that the above technical solution is known to those skilled in the art as it is described in the background of the present disclosure.
Documents advantageous to the understanding of the present disclosure and conventional technologies are listed below, and are incorporated herein by reference, as they are fully described in this text.    Non-patent document 1: 3GPP TS 36.331 V11.3.0(2013-03) Radio Resource Control (RRC) specification. (Release 11);    Non-patent document 2: 3GPP TS 36.321 V11.2.0(2013-03). Medium Access Control (MAC) protocol specification (Release 11); and    Non-patent document 3: 3GPP TS 36.300 V11.5.0(2013-03) Overall description (Stage 2). (Release 11).